Breastmilk can be mixed together from two different pumpings, as long as the milk is the same temperature. So, if you have some bottled milk stored in the fridge and wish to add a new batch, wait until the new batch has been cooled in the fridge then mix the two batches together. The new, warmer milk should not be mixed with the colder stored milk.

You will notice that breastmilk will separate into two layers. The fatter part of the breastmilk has risen to the top the same as when we have whole cow’s milk and the cream rises to the top. A quick shake before using mixes it all together again.